Noncontaminative centrifugal pump

ABSTRACT

The present invention relates to a noncontaminative centrifugal pump for pumping a high-purity liquid, such as a high-purity chemical or ultrapure water used in a VLSI circuit manufacturing system, without producing any trace of dust and without allowing foreign matters entering its casing. A noncontact shaft seal assembly provides an accurate gap between the rotating and fixed rings thereof to allow a required leakage from the noncontaminative centrifugal pump, does not produce dust by abrasion, inhibits foreign matters from entering the noncontaminative centrifugal pump and maintains the high-purity liquid in a high-purity condition. While the noncontaminative centrifugal pump is in operation, the impeller produces a hydraulic axial thrust to bias the main shaft in one direction by a distance equal to a play thereof so that the gap is maintained in a set size suitable for preventing generation of dust by abrasion and inhibiting foreign matters from entering the casing. The position of the fixed ring of the shaft seal assembly can be adjusted from outside to adjust the gap to a size suitable for maintaining an optimum leakage while the noncontaminative centrifugal pump is in operation. The noncontaminative centrifugal pump facilitates work for inspection and maintenance and is suitable for pumping a high-purity liquid.

TECHNICAL FIELD

The present invention relates to a pump for pumping a high-purityliquid, such as a high-purity chemical or ultrapure water used in a VLSI(very large scale integrated) circuit manufacturing system, withoutinternally producing any trace of dust and, more specifically, to anoncontaminative centrifugal pump provided with a noncontact shaft sealassembly providing an accurate gap to allow a required leakage from theassociated system, and having a structure that does not produce dust byabrasion and inhibits foreign matter from entering the casing of thenoncontaminative centrifugal pump.

BACKGROUND ART

Generally, in a centrifugal pump for pumping pure water or the like, theentire wetted surfaces of the component parts are finished by grindingto increase impurity eliminating accuracy, and the component parts areformed of materials of an appropriate grade to prevent ionization.However, as regards the shaft seal assembly, a rotating ring is pressedwith a spring against a fixed ring in sliding contact, tolerating theproduction of particles by abrasion as a natural result, and effortshave been entirely devoted to eject the particles produced by abrasionfrom the system. Although research on materials for formingabrasion-resistant surfaces are made, such materials are expensive andthere is little prospect of successfully constructing a noncontaminativepump using such expensive materials.

Such a prior art centrifugal pump has been satisfactorily employed inthe field where a liquid of a purity of: a comparatively low level isused. However, the prior art centrifugal pump is unsatisfactory for usein a system that handles a liquid of a very high purity, such as anultrapure water system, and unsolved problems still reside therein.

It is an object of the present invention to provide a centrifugal pumpof an ordinary, simple construction, eliminating plays in bearings byusing a hydraulic thrust produced by the pressure produced by animpeller, provided with a shaft seal assembly forming a gap of anadjusted size between slipping surfaces, facilitating maintenance andinspection and conforming to requirements for pumping a high-purityliquid.

DISCLOSURE OF THE INVENTION

The present invention provides a noncontaminative centrifugal pump forpumping a high-purity liquid, such as a high-purity chemical orultrapure water used in VLSI circuit manufacturing systems withoutproducing any trace of dust. A pump in accordance with the presentinvention comprises a casing 1, a rotor comprising an impeller 5 and amain shaft 6, and a shaft seal assembly disposed in a portion of thecasing 1 through which the main shaft penetrates the casing 1 andcomprising a rotating ring 8a that rotates together with the rotor, anda fixed ring 8b disposed fixedly opposite to the rotating ring 8a. Thefixed ring 8b is fixed to a seal case 9, and the seal case 9 is fittedin a boss of the casing 1 and connected to the casing 1 by screw threadengagement or the like so as to be movable relative to the casing 1 forpositional adjustment to adjust the size of a gap e between the slippingsurfaces properly without disassembling the pump while the pump is inoperation as well as while the pump is stopped and to be fixed afterpositional adjustment.

The impeller 5 has main impeller vanes 5a for applying pressure to theliquid with centrifugal force, and outvanes 5b for counterbalancing anaxial thrust generated by the produced pressure and acting on theimpeller 5. The outside diameter and the shape of the outvanes 5b aredesigned so that an axial thrust acts in one direction on the impeller5. This axial thrust biases the main shaft 6 in one direction to removea play attributable to clearances between the components of a bearing12, such as a ball bearing, and holds the main shaft 6 stably at anappropriate position to secure stably the gap e between the respectiveslipping surfaces of the rotating ring 8a and the fixed ring 8b in anappropriate size. The position of the seal case 9 is adjusted properlyso that the sliding surfaces are not in contact with each other and anappropriate leakage is secured. Therefore, the shaft seal assembly doesnot produce any dust by abrasion, and any foreign matters are notadmitted into the pump, whereby the quality of high-purity liquid ismaintained. Naturally, the wetted components including the casing 1 andthe impeller 5 are finished properly for impurity removal byconventional finishing techniques including precision machining,mirror-finish polishing and supercleaning.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal sectional view of a noncontaminativecentrifugal pump of a preferred embodiment according to the presentinvention;

FIG. 2 is a cross-sectional view of an impeller section of thenoncontaminative centrifugal pump, as viewed from the suction side;

FIG. 3 is a fragmentary longitudinal sectional view showing a shaft sealassembly and flows of a liquid generated by an impeller included in thenoncontaminative centrifugal pump; and

FIG. 4 is a fragmentary longitudinal sectional view of a modification ofthe noncontaminative centrifugal pump of FIG. 1, in which a rotatingring is disposed on the side of the atmosphere with respect to a fixedring.

BEST MODE FOR CARRYING OUT THE INVENTION

A mechanical seal assembly, i.e., a conventional shaft seal assemblyemployed in pumps of the type pertaining to the present invention has arotating ring and a fixed ring pressed against each other with a springin sliding contact for sealing. The present invention, differing intechnical idea from such a conventional mechanism, forms a gap betweenthe slipping surfaces of a rotating ring and a fixed ring to keep therotating ring and the fixed ring separated from each other and to allowa controlled leakage through the gap, so that no dust is produced byabrasion, external impurities are inhibited from entering the casing andthe liquid is maintained in a high-purity liquid condition.

Referring to FIG. 3, upon start of operation of a noncontaminativecentrifugal pump after adjusting the position of a seal case 9 so that agap e of a set size is formed between the slipping surfaces of arotating ring 8a and a fixed ring 8b, a small flow (leakage) is producedfrom a suction opening a through the circumference b of an impeller 5,the back side c of the impeller 5, a central portion d of the back sideof the impeller 5 and the gap e to a recovery line f when a pumping flowis produced from the suction opening a through the circumference b ofthe impeller 5 to the discharge opening, not shown. A portion of theliquid of a pressure Pb flowing along the circumference of the impeller5 flows along the back side c of the impeller 5 against a centrifugalforce toward the central portion d of the back side c of the impeller 5,and the pressure of the portion of the liquid decreases to a pressurePd. The portion of the liquid of the pressure Pd leaks through the gap eand is discharged to the outside of the system through the recovery linef.

A main shaft 6 can be positioned with a certain accuracy by theconventional technique that limits clearances between the components ofa bearing 12, such as a ball bearing, by preloading the bearing 12.According to the present invention, the pressure difference between thepressure Pb prevailing around the circumference b of the impeller 5 anda pressure Pc prevailing in the vicinity of the back side c of theimpeller 5 by outvanes 5b acts as a hydraulic axial thrust to the left,as viewed in FIG. 3, on the main shaft 6 to inhibit the play of the mainshaft 6 attributable to the clearances between the components of thebearing 12 supporting the main shaft 6 and, consequently, the axialposition of the main shaft 6 can be very accurately stabilized, so thatthe appropriate size of the gap e between the rotating ring 8a and thefixed ring 8b can be stably secured.

The size of the gap e can be adjusted during the operation of thenoncontaminative centrifugal pump. The leakage through the gap e ismonitored through observation of the flow of the liquid through therecovery line f, the axial position of a seal case 9 is adjusted withoutstopping the noncontaminative centrifugal pump so that a set leakage issecured, and then the seal case 9 is fixed relative to a casing 1 with aset screw 11.

A preferred embodiment of the present invention will be described indetail with reference to the accompanying drawings. FIG. 1 is alongitudinal sectional view of a noncontaminative centrifugal pump of apreferred embodiment according to the present invention, showing acasing 1, a series of stationary parts including a bearing support 4, arotor comprising a main shaft 6 and an impeller 5 mounted on the mainshaft 6, and a rotating ring 8a of a shaft seal assembly disposed on theside of the liquid with respect to the fixing ring 8b.

FIG. 2 shows the casing 1 and the impeller 5 of the noncontaminativecentrifugal pump embodying the present invention. The wetted componentparts are designed in shapes capable of being precisely finished byturning or the like. For example, the impeller 5 is of a semiopen typeand portions of the volute casing 1 are formed in concentric circularshapes, respectively, and are entirely subjected to mirror-finishgrinding (electropolishing), etc. and supercleaning. Thenoncontaminative centrifugal pump is designed so that pockets in whichthe liquid stagnates are reduced to the least possible extent. Adischarge pipe 2 is formed separately from the casing 1 to enable theperfect grinding of a discharge diffusing portion, which is narrow whenthe noncontaminative centrifugal pump is of a small capacity. Thedischarge pipe 2 is finished by grinding and is fastened to the casing 1with an O-ring 14 disposed between the casing 1 and the discharge pipe 2for sealing. Thus, the discharge pipe 2 can be removed from the casingfor cleaning.

FIG. 3 shows the details of a shaft seal assembly and flows of theliquid produced by the impeller 5. The fixed ring 8b is fastened to theseal case 9 with a holding member 10, the seal case 9 is held in thecasing 1 in screw engagement with an O-ring 16 between case 9 andcasing 1. The seal case 9 is moved axially for fine positionaladjustment to form a gap e of an optimum size for a set leakage.

The outvanes 5b of the impeller 5 are designed so that an axial thrustacts to the left, as viewed in FIG. 3, on the main shaft 6. When thenoncontaminative centrifugal pump operates, the main shaft 6 is shiftedto the left, as viewed in FIG. 3, and the size of the gap e in astationary state is reduced to an appropriate size so that the leakageis adjusted properly to the least necessary value. When thenoncontaminative centrifugal pump is stopped, the size of the gap eincreases slightly and the leakage increases slightly, which isdesirable for the purpose of inhibiting foreign matters from enteringthe noncontaminative centrifugal pump. However, when increase in theleakage needs to be suppressed, it is possible to limit the leakage to adesired value while the noncontaminative centrifugal pump is stopped bya conventional technique, for example, by providing the pumping systemwith an automatic regulating valve in connection with thenoncontaminative centrifugal pump. The outvanes 5b may be designed, whenrequired, so that an axial thrust that acts to the right on the mainshaft 6 is produced. When the axial thrust acts to the right, theleakage is limited to the least value while the noncontaminativecentrifugal pump is stopped and the leakage increases slightly when thenoncontaminative centrifugal pump operates.

FIG. 4 shows a noncontaminative centrifugal pump of another embodimentaccording to the present invention, in which a rotating ring 8a isdisposed on the side of the atmosphere with respect to a fixed ring 8b,and the components are designed so that an axial thrust acting to theright is produced when the noncontaminative centrifugal pump operates.The effects of the disposition of the rotating ring 8a on the side ofthe atmosphere with respect to the fixed ring 8b is the same as that ofthe rotating ring 8a on the side of the liquid with respect to the fixedring 8b as shown in FIG. 3, and the direction of action of the axialthrust may be altered. The rotating ring 8a is mounted on a sleeve 7provided with a shoulder 7a and is pressed against the shoulder 7a witha spring 8c to prevent abnormal contact between the slipping surfaces ofthe rotating ring 8a and the fixed ring 8b due to an erroneous operationfor adjusting the position of a seal case 9 and to inhibit wobblingmotion of the rotating ring 8a.

Although an impeller 5 is fixed directly to a main shaft 6 with anO-ring 15 therebetween by screwing the impeller 5 on the main shaft 6 inthese embodiments shown in FIGS. 3 and 4, the impeller 5 may of coursebe keyed to the main shaft 6 to transmit the torque of the main shaft tothe impeller 5 and may be fixed to the main shaft 6 with a nut.

The shapes and the materials of the rotating ring 8a and the fixed ring8b may be optionally selected according to the purpose of thenoncontaminative centrifugal pump, provided that the respective slippingsurfaces of the rotating ring 8a and the fixed ring 8b can be accuratelymachined and finished. Naturally, the members of a general mechanicalseals may be applied to the rotating ring 8a and the fixed ring 8b. Thesleeve 7 may be omitted and the rotating ring 8a may be mounted directlyon the main shaft 6. It is to be understood that the present inventionmay be practiced otherwise than as specifically described herein withoutdeparting from the scope and spirit thereof.

INDUSTRIAL APPLICABILITY

As is apparent from the foregoing description, the noncontaminativecentrifugal pump in accordance with the present invention has a simpleconstruction, can be manufactured at comparatively low manufacturingcosts, facilitates work for inspection, adjustment and so on, therotating ring and the fixed ring of the shaft seal assembly are held ina noncontact state with a gap therebetween to allow a set leakagethrough the gap outside therefrom, does not produce any dust therein,inhibits foreign matters from entering therein and is capable ofinsuring the high-purity quality of the liquid. Thus, thenoncontaminative centrifugal pump of the present invention can beeffectively applied to pumping a high-purity liquid, such as high-puritychemicals, and ultrapure water for use on a VLSI circuit manufacturingline.

What is claimed is:
 1. A non contaminative centrifugal pump for pumpinga high purity liquid, comprising:a casing; a rotatable main shaftextending through said casing; a shaft seal assembly between said casingand said main shaft, said shaft seal assembly including a rotating ringmounted on said main shaft and a fixed ring mounted on said casing, saidrotating ring and said fixed ring being disposed to be separated fromone another, axially of said main shaft, to define therebetween a gapwhich is maintained both during operation and stoppage of the pump toallow liquid to leak through the gap and outside the pump even duringthe operation of the pump; rolling bearing means rotatably supportingsaid main shaft and having therein an inherent small clearance which isabsorbed when the main shaft is shifted in an axial direction thereof;and an impeller fixedly mounted on said main shaft and having aconfiguration to exert a hydraulic thrust force against said main shaftand bias said main shaft in axial direction when the pump is inoperation, thereby to shift said main shaft and said rotating ring insaid axial direction by a distance corresponding to said clearance andthereby to fix said main shaft in said axial direction, so that said gapis set at an exact predetermined value during the operation of the pumpto allow a predetermined amount of leakage of the liquid through saidgap to the outside of the pump and thereby prevent generation of dust byabrasion of said rotating and said fixed rings and also inhibit entry offoreign matter into said casing.
 2. A noncontaminative centrifugal pumpaccording to claim 1, wherein said fixed ring is mounted to be shiftableaxially of said main shaft relative to said casing for fine positionaladjustment of said gap.
 3. A noncontaminative centrifugal pump accordingto claim 2, comprising a structure on which said fixed ring is mountedon said casing, said structure being shiftable relative to said casingand axially of said main shaft for fine adjustment.
 4. Anoncontaminative centrifugal pump according to claim 1, wherein saidrotating ring is disposed between said impeller and said fixed ring, andsaid impeller is configured to exert said hydraulic thrust force towardsaid fixed ring.
 5. A noncontaminative centrifugal pump according toclaim 1, wherein said rotating ring is disposed between said impellerand said fixed ring, and said impeller is configured to exert saidhydraulic thrust force away from said fixed ring.
 6. A noncontaminativecentrifugal pump according to claim 1, wherein said fixed ring isdisposed between said impeller and said rotating ring, and said impelleris configured to exert said hydraulic thrust force away from said fixedring.
 7. A noncontaminative centrifugal pump according to claim 1,wherein said fixed ring is disposed between said impeller and saidrotating ring, and said impeller is configured to exert said hydraulicthrust force toward said fixed ring.
 8. A noncontaminative centrifugalpump according to claim 1, wherein said rotating ring is supported onsaid main shaft so as to be shiftable axially of the main shaft againsta resilient force.
 9. A noncontaminative centrifugal pump according toclaim 1, wherein said rolling bearing means limits the axialdisplacement of said main shaft and said rotating ring, due to saidhydraulic thrust, to said small clearance in the rolling bearing meansto prevent further axial displacement of said rotating ring towards saidfixed ring and preserve said exact predetermined value of said gapduring the operation of said pump.
 10. A noncontaminative centrifugalpump for pumping a high purity liquid, comprising:a casing; a rotatablemain shaft extending through said casing; a shaft seal assembly betweensaid casing and said main shaft, said shaft seal assembly including arotating ring mounted on said main shaft and a fixed ring supported bysaid casing with capability of fine positional adjustment in axialdirections of said main shaft, said rotating ring and said fixed ringbeing disposed to be separated from one another, axially of said mainshaft, to define therebetween a gap which is maintained both duringoperation and stoppage of the pump to allow liquid to leak through thegap and outside the pump even during the operation of the pump; rollingbearing means rotatably supporting said main shaft and having therein aninherent small clearance in axial direction of the shaft which isabsorbed when the main shaft is shifted in an axial direction thereof;and an impeller fixedly mounted on said main shaft and having aconfiguration to exert a hydraulic thrust force against said main shaftand bias said main shaft in said axial direction when the pump is inoperation, thereby to shift said main shaft and said rotating ring insaid axial direction by a distance corresponding to said clearance insaid rolling bearing means and thereby to maintain said main shaftimmovable in said axial direction, so that said gap is set at an exactpredetermined value during the operation of the pump to allow apredetermined amount of leakage of the liquid through said gap to theoutside of the pump and thereby prevent generation of dust by abrasionof said rotating and said fixed rings and also inhibit entry of foreignmatter into said casing.
 11. A noncontaminative centrifugal pumpaccording to claim 10, comprising a positional adjustment structurethrough which said fixed ring is supported on said casing, saidpositional adjustment structure being mounted on said casing foradjusting the fixed ring with respect to said axial direction of themain shaft.
 12. A noncontaminative centrifugal pump according to claim11, wherein said positional adjustment structure comprises a seal casewhich fixedly secures said fixed ring thereon and is in screw engagementwith said casing for effecting said fine positional adjustment in theaxial directions of the main shaft.
 13. A noncontaminative centrifugalpump according to claim 12, wherein said seal case is screw adjustable,from outside, relative to said casing.
 14. A noncontaminativecentrifugal pump for pumping a high purity liquid, comprising:a casing;a rotatable main shaft extending through said casing; bearing meansrotatably supporting said main shaft; a shaft seal assembly between saidcasing and said main shaft, said shaft seal assembly including arotating ring mounted on said main shaft and a fixed ring supported bysaid casing, said rotating ring and said fixed ring being disposed to beseparated from one another, axially of said main shaft, to definetherebetween an axial gap which is maintained both during operation andstoppage of the pump to allow liquid to leak through the gap and outsidethe pump even during the operation of the pump; and adjusting meansinterposed between said fixed ring and said casing for fine positionaladjustment of the fixed ring relative to said casing in axial directionsof said main shaft; whereby said axial gap is set at a predeterminedvalue during both operation and stoppage of the pump to allow apredetermined amount of leakage of the liquid through said gap to theoutside of the pump and thereby prevent generation of dust by abrasionof said rotating and said fixed rings and also inhibit entry of foreignmatter into said casing.
 15. A noncontaminative centrifugal pumpaccording to claim 14, wherein said adjusting means comprises a sealcase which fixedly secures said fixed ring thereon and is in screwengagement with said casing for fine positional adjustment in said axialdirections of the main shaft.
 16. A noncontaminative centrifugal pumpaccording to claim 15, wherein said seal case is screw adjustable fromoutside relative to said casing.